Implement Gas Exactimation

[juli]

RSKj does not implement the binary search solution implemented by geth and parity in eth_estimateGas, some transactions can fail unexpectedly with OOG.

Truffle Suite recently published a less CPU intensive solution they called Gas Exactimation

Latest implementation: https://github.com/trufflesuite/ganache-core/blob/3ec34fe972dc17a5600eb566c8c309cd5ddb38bd/lib/utils/gasEstimation.js

This issue will be more relevant if RSKj implements EIP-150 63/64 rule (#944)

[joaquinlpereyra-iov]

The problem with our current implementation is that it does take into account gas-returning OPCODES like SUICIDE, returning the gas used, not the gas you must send.

So if you use the gas returned by eth_estimageGas, you may get OOG.

[SergioDemianLerner]

Also does not take into account gas refunds because of SSTORE changes.
And also gas amounts locked by CALL and the 2300 pre-send amount required by CALLs with value.

My suggestion to solve this issue is to code Gas Exactimation [but it must be analyzed for correctness, because it's written mainly for Ethereum and the 63/64 rule]:

OR, as a simpler alternative that will work 99.99% of the time (I'm trying hard to find examples where this wouldn't work):

• Change TransactionExecutor to return not only the gas consumed but also the gas paid in advance before refunds.

• Add 2300 to the transaction limit IF there is any CALL at non-top level that transfers value.

[SergioDemianLerner]

PR with gas exactimation method here #990

[SergioDemianLerner]

I'm analyzing this issue deeper since I discovered that the previous code already skips refunds using the localCall variable when estimating gas (in a very ugly way). This is good news (the previous code works in most cases) and bad news (the previous code sucks).

[SergioDemianLerner]

I detected another problem with estimateGas(). It does not differentiate between an OOG exception and a successful finalization. Therefore the gas limit passed to estimageGas() should always be higher than the actual gas consumed. By doing that one can differentiate the cases: returnedValue==gasLimit means OOG.

[SergioDemianLerner]

New code in the PR ready. Tests passed and all ready to go.
I identified the simple case where the previous estimation would fail. Solidity code is this:

function () external payable { }
function callWithValue() public payable {
address(this).transfer(100);
}

The old estimator would estimate 2300 less units of gas than the required to properly execute the method callWithValue().

[pmprete]

This issue is still relevant, and is causing #1279